Altec 1505B + TAD 4001

[rubjel]

Greetings from Norway, I'm a new user on this great forum!

I have done lots of reading on this forum for the past 15 years, finally it's time for me to make a post :)
I know there are lots of knowledgeable people here, so I hope someone can help me out.

So I want to make throat adapters to fit my 2" exit TAD 4001 to Altec 1505B horns. Question is, how long should this adapter be?
I have a pair of original Altec 30166 adapters to use with my 1.4" exit Altec 288-16G drivers. These are 190mm length.

The TAD 4001 have a 10 degree exit angle, according to my calculations the adpater would have to be approximately 130mm length to keep the same flare angle as the original.
However since the 4001 has a wider exit angle than Altec 288, maybe the throat adapter should also have a wider angle than the original adapter for a smoother transition to the horn?
In that case it would have to be even shorter than 130mm..

I'm a bit confused about this, so hopefully someone with a better understanding than me will chime in.

Regards,
Rune

[Bonzo75]

Hi Rune, if you get Markus klug's wooden 1505, you can get adapters made for any of drivers... Tad, Radian, etc. You can contact him off Facebook.

[rubjel]

Hi Rune, if you get Markus klug's wooden 1505, you can get adapters made for any of drivers... Tad, Radian, etc. You can contact him off Facebook.

Hi Bonzo, thank you very much for your reply!

I have in fact been in contact with Markus, and he suggested 150mm length for the 2" adapter because there seems to be information from someone that Altec made a 2" adapter of this length.
However I have never found any reference to such an adapter, so I wanted to investigate for myself what the correct length would be. I think it should be shorter than this to get the same ratio of expansion compared to the 288 adapter. Doesn't seem to be much experience abot this topic among the users of this forum, I would have thought there is quite a number of users with multicells and 2" exit drivers.

[Bonzo75]

I know one guy on Facebook whom I visited in Paris to listen to his Markus klug multicell with Radian 950pb Be, which is 2 inch. But I can't help you with any technical know-how behind that.

[speakerdave]

Consider starting with the JBL 2328 2" throat to handle the transition from round to rectangular cross section and building a wooden adapter to tie together the two rectangles of the throat exit and the horn entrance. You would need the dimensions of the horn entrance and the 2328 exit, the relative size and the aspect ratio of both; the latter are available in these forums. Beyond this basic idea I cannot offer any more help. You would need to work out an exponential expansion, I think. You could possibly use the termination of your Altec throat as a model for the angles they used at the horn entrance. A little fudging may be unavoidable; try to make smooth transitions. The 2328's are neither rare nor common, but usually available somewhere on the used market.

You should also be aware that the TAD 4001 when used on its stock horn requires compensation in the high pass of the crossover to deal with an upper treble peakiness.

[rubjel]

I know one guy on Facebook whom I visited in Paris to listen to his Markus klug multicell with Radian 950pb Be, which is 2 inch. But I can't help you with any technical know-how behind that.

Hi Bonzo, thats very interesting! Did you like what you heard from this combination? Were they 15 cell horns?
The 950 has a very short throat, so I would think they are more optimal for use with a rapidly flaring horn. But sometimes theoretically mismatched combinations work very well :)


Consider starting with the JBL 2328 2" throat to handle the transition from round to rectangular cross section and building a wooden adapter to tie together the two rectangles of the throat exit and the horn entrance. You would need the dimensions of the horn entrance and the 2328 exit, the relative size and the aspect ratio of both; the latter are available in these forums. Beyond this basic idea I cannot offer any more help. You would need to work out an exponential expansion, I think. You could possibly use the termination of your Altec throat as a model for the angles they used at the horn entrance. A little fudging may be unavoidable; try to make smooth transitions. The 2328's are neither rare nor common, but usually available somewhere on the used market.

You should also be aware that the TAD 4001 when used on its stock horn requires compensation in the high pass of the crossover to deal with an upper treble peakiness.

Thanks Dave, that's a very good suggestion starting with the JBL 2328 throat adaptors!
They are very short though, I am in the process of having some similar throat adaptors made for the B&C DCM50 driver to try on the 1505 horns. The DCM50 are a throatless design, so I made drawings for a very short adaptor for them, basically just a transition from circular to rectangular cross section.

I am wondering if the length of the adaptor will have a significant impact on low frequency loading, basically supporting longer wavelengths to be horn loaded..
Maybe there is an optimal compromise between this and transition angle from driver throat to horn expansion?

Regarding the TAD 4001, you are absolutely right, there is a harhness in the upper treble region that needs to be tamed. Cone breakup resonances I guess, although I thought these would be even higher for a beryllium diaphragm.
I have been using some Yamaha JA6681B drivers lately that I actually like better than the 4001. Very surprising, I have had them laying around for a couple of years without testing them until now. These don't have any annoying artifacts in the treble, and can use the same throat adaptor as the Altec 288.

[speakerdave]

I think the mass breakup point of beryllium is theoretically 15k or so. Whatever the problem was in the 4001, it was fixed in the 4003 (and 2002). There are hints in the literature about mechanical resonances in the joining of materials in the diaphragm.

The high pass circuit of the TN-2 is out there on the web, I believe. The 4001 is no slouch.

[Bonzo75]

Hi Rubjel, difficult to say. My reference for Radian is the horns Universum which is in the autotech 200T JMLC made by the same guy who makes the universum

With this particular horn, I did not get the same sound but that could have been to crossovers too, can't say if it was due to difference between multicell or JMLC. Also this particular multicell was touching the sidewalls which is not the optimum position for multicell. So I don't think it was a demo I could judge on.

For TAD 4001 my listening to Cessaro gamma, and spending time with DIYers suggests that use JMLC 350 and then cross over to 2001 to avoid the resonance peaks in JMLC 2500

[jblguy]

I'm slightly late to the gate but I have some in cast metal. A fellow in Europe forged me a set to fit 2 inch drivers. They look like an original Altec but for 2 inch throat driver. I needed them for my 1505 to use a 2 inch driver. I used a TAD 4002 and it sounds great. Trouble is I can't find the info or the emails of the guy the did it for me. Opps shit.

[jblguy]

I'm slightly late to the gate but I have some in cast metal. A fellow in Europe forged me a set to fit 2 inch drivers. They look like an original Altec but for 2 inch throat driver. I needed them for my 1505 to use a 2 inch driver. I used a TAD 4002 and it sounds great. Trouble is I can't find the info or the emails of the guy the did it for me. Opps shit.
Ok UPDATE
I did find my old info. It was seller in Europe who was on Ebay. He made forged throats for horns. He special made me a set for the 1505 to fit 2 inch 4 bolts drivers. cost was $400. per pair. This was in 2012. Doesn't seem to be on Ebay currently.

[mwaldron]

I don't get to add value to this forum very often, but on this subject I just finished watching two different conversations with Greg Timbers where he touches on this very subject. I think it is the second one he goes into depth on the evolution of the driver to horn transition designs and how to use modern technologies to streamline the process, they are long but very worthwhile conversations to have the liberty to watch and hear.

https://youtu.be/afeTHLLp-EI

[Ian Mackenzie]

My suggestion would be to contact Jonathan Weiss at OMA as they deal with a lot of these early Altec horns. He might have made up some adapters.

On the Tad 4001 my recollection is that the 4001 was set up for the TH4001 horn for a flat response. This was according to Bruce Edgar who questioned why the 4001 was aggressive. Perhaps there was some losses with the finned TAD radial horn and Tad did something to the 4001 to compensate for their horn. I vaguely recall the finless Yuichi horn having a rising response in the top octave on Yuchi’s website with the 4001.

[dn92]

My suggestion would be to contact Jonathan Weiss at OMA as they deal with a lot of these early Altec horns. He might have made up some adapters.

On the Tad 4001 my recollection is that the 4001 was set up for the TH4001 horn for a flat response. This was according to Bruce Edgar who questioned why the 4001 was aggressive. Perhaps there was some losses with the finned TAD radial horn and Tad did something to the 4001 to compensate for their horn. I vaguely recall the finless Yuichi horn having a rising response in the top octave on Yuchi’s website with the 4001.

Response of TD-4001 on TH4001 is not flat on axis, this why there is an EQ in the TN-1/TN-2 and TN-3 crossovers. This EQ is done by two RLCs working together. This enables a better response on axis, but still not flat in order not to touch too much the off axis response. It is a compromise. Correctly filtered TD-4001 on TH-4001 has nothing aggressive. TD-4002 has almost the same response.
Arai290 is a bit different, in particular at the transition piece from compression throat to horn, rectangular for TAD, squared for Arai, providing higher level in high frequencies, that is not necessary.